Depends on what you want to do with the deck. You seem to want to go Aggro based on your title, so any creature 5-cmc and over is immediately out.

More Blood Crypts and adding Dragonskull Sumits would be good to fixing your mana base. Other than that, 23 lands is about where you want to be, with the Mountain/Swamp split depending entirely on how much Red VS Black you want/need at any given turn.

Now, as far as creatures do, you want a lot of Aggressive cards, Rakdos Cackler, Grave Crawler, basically you're looking at all the 2 power 1 cost creatures in Red and Black. You'll ideally want between 10 and 14 pf them, depending how Aggressive you want your early game VS how much staying power you want. Stromkirk Noble is another to look at because he get's pretty big by just doing what you want to do.

Are isn't much in the way of 2-drops, but Knight of Infamy, Shred-Freak, Gore-House Chainwalker and Ash Zealot are really what you want to look at, with maybe Crimson Muckwader if you're looking to be more heavy into Black than Red. You'll wand between 4 and 8, again depending on how aggressive you want to be early in the game.

3-drops, sadly doesn't have much going for it. Guttersnipe is good if you've got 16+ removal spells for it. Geralf's Messenger if you happen to be VERY heavy in Black. Hellhole Flailer is pretty good if you're a little slower of a deck.

Cryptborn Horror is terrible since you can't play it if you havn't dealt damage that turn.

As far as other spells go, Pillar of Flame and Searing Spear are pretty much required as auto 4-ofs. You can run some Dynacharge to pump your horde of small guys, but I like to round it out with more removal.

Stuff like Traitorous Blood is better left in the SB since it's really only needed VS creatures you can't remove or can't trade with favorably in combat/with removal (ie: Thragtusk).

Consistancy is key, which means having a lot of 4 and 3 copies of your more agressive cards, and fewer for cards that you might not what to see in every game, but want to have access to during game 1.

I do not care for that six cost demon in a 22 land deck. I wouldn't be comfortable running anything more then 4 in this, tbh. No reason to slow yourself down. I'd lose those two demons and 4 of the removal spells for at least two more 1-drops and maybe Gore-House Chainwalker as a decent 2-drop addition.

In my opinion Nefarox, Overlord of Grixis doesnt fit so well. If you want an aggro deck, you dont want to be attacking with a single creature, you want to keep coming at your opponent at every turn, exalted is the total opposite of that. There are better demons to stick in his place ex: Desecration Demon or Rakdos, Lord of Riots